Filamentary cathode support



Oct. 21, 1941; c. T. MILLER FILAMENTARY GATHODE SUPPORT Filed Sept. '7, 1940 INVENTOR CHARLES 7. MILLER a? Qu r ATTORNEY Patented Oct. 21, 1941 UNITED STATES FILAMENTARY CATHODE SUPPORT Charles T. Miller, Newark, N. J assignor to Radio Corporation of America, a corporation of Delaware Application September 7, 1940, Serial No. 355,741

2 Claims.

My invention relates to electron discharge devices, particularly to means for mounting vibration free filamentary cathodes in such devices.

The usual electrode assembly of the modern electron discharge device comprises two parallel insulating spacers secured to the ends of concentric anode, grid and cathode electrodes. Filamentary cathodes stretched between the spacers along the axis of the tube are subject to vibration and means proposed for damping the vibration usually comprises an insulated wire hook welded to the grid side rod and engaging the center of the filament. This wire hook, however, cannot be attached to the side rod after the anode has been placed around the grid and if attached before the electrodes are assembled it is difficult to thread the cathode filament through the bight of the hook because of its small size. In very small tubes, particularly, where the sides of the grid may be less than .020 to .030 inch apart, the hook in the wire must be so small that insulation sprayed on the wire would fill the bight.

An object of my invention is an improved electrode assembly with a filamentary cathode in which the cathode may be easily assembled and in which the cathode is damped against vibration.

A more specific object of my invention is an improved vibration damper for filamentary cathodes.

Characteristic features of my invention are defined in the appended claims and one embodiment is described in the following specification and shown in the accompanying drawing in which Figure 1 is an elevational view, partly in section, of an electrode assembly with a filamentary cathode and my improved filament damper, Figure 2 is a perspective fragmentary view of my improved filament damper and Figure 3 is an end view of a grid assembled with my improved filament damper.

The electrode assembly of the tube shown in Figure 1 comprises filamentary cathode I, fiattened tubular grid 2 and anode 3 supported at their ends and insulatingly spaced by spacers 4 and 5. The cathode is a fine wire of refractory metal, preferably oxide coated, and tautened between its two lead-in conductors 6 by spring support I which draw the wire into the corners of triangular openings 8 and 9 in the spacers to center the filament between the sides of the grid. The grid is tubular with parallel spaced side rods and flattened convolutions of grid wire. The grid wire may be a single piece spirally wound on the side rods or short parallel lengths of wire attached at their ends to the side rods.

In manufacture it is necessary first to assemble the grid and anode with their spacers 4 and and then to thread the filament into the spacer openings and through the grid and secure its ends to the lower lead-in conductor 6 and spring I.

Where the filament may be .001 inch wire covered with a loose, friable coating of barium-strontium carbonates, it is particularly desirable that the filament be inserted without scraping and without kinking the wire. Means to dampen vibration of the filament according to my invention comprises a straight round rod or bar of insulation I0 extending transversely through the grid and preferably half way between the sides of the grid and about mid-way between the ends of the grid. In threading the filament through the grid the filament wire may pass on either side of the damper bar l0 and may be pulled tight over the smooth sides of the bar without damage to the coating on the filament. Since the sides of the damper bar in contact with the filament, are parallel and normal to the plane of the grid, the filament is drawn into a central position between the two sides of the grid when the filament is tautened. The round insulated damper bar may conveniently comprise a short V-shaped piece of wire I I, one leg of which is sprayed and the other leg of which is welded to the side rod. By sighting along the axis of the grid it is comparatively easy to find the central transverse position for the damper bar and to then secure the bar in place by spot welding the wire H to the side rod.

In making tubes of the type commercially known as the IE5 good results have been obtained in fastening a damper bar of alumina or alundum sprayed on a nickel wire and welded to the side rod of a wire wound flattened grid only .026 inch between sides and .110 inch between side rods. The displacement of the filament wire toward either side rod parallel to the grid wires by the damper bar has no effect upon the electrical characteristics of the tube.

My improved electrode assembly with filamentary cathode is easily assembled and the cathode is dampened against vibration.

I claim:

1. In combination a tubular grid with a s de rod and a plurality of turns of wire attached to the side rod, a filament extending axially of the grid turns, a damper bar for steadying the filament comprising an insulated rod attached to the side rod and extending transversely across the center of the grid intermediate the ends of the grid and bearing along one of its straight sides against said filament.

2. A grid assembly comprising two parallel spaced side rods, flattened convolutions of grid wires attached to the side rods, an insulating bar attached to one side rod intermediate the ends of the rod extending between the flattened sides of the grid and normal to the plane of the fiattened grid wire convolutions.

CHARLES '11,. MILLER. 

